{-# LANGUAGE TemplateHaskell, Rank2Types, NoMonomorphismRestriction #-}
-----------------------------------------------------------------------------
-- |
-- Module      :  Main
-- Copyright   :  (C) 2012 Edward Kmett, nand`
-- License     :  BSD-style (see the file LICENSE)
-- Maintainer  :  Edward Kmett <ekmett@gmail.com>
-- Stability   :  provisional
-- Portability :  TH, Rank2, NoMonomorphismRestriction
--
-- A simple game of pong using gloss.
-----------------------------------------------------------------------------
module Main where

import Control.Applicative ((<$>), (<*>))
import Control.Lens
import Control.Monad.State (State, execState, get)
import Control.Monad (when)

import Data.Set (Set, member, empty, insert, delete)
import Data.Set.Lens (contains)
import Data.Pair.Lens (both)

import Graphics.Gloss
import Graphics.Gloss.Interface.Pure.Game

import System.Random (randomRs, getStdGen)

-- Some global constants

gameSize        = 300
windowWidth     = 800
windowHeight    = 600
ballRadius      = 0.02
speedIncrease   = 1.2
losingAccuracy  = 0.9
winningAccuracy = 0.1
initialSpeed    = 0.6
paddleWidth     = 0.02
paddleHeight    = 0.3
paddleSpeed     = 1
textSize        = 0.001

-- Pure data type for representing the game state

data Pong = Pong
  { _ballPos   :: Point
  , _ballSpeed :: Vector
  , _paddle1   :: Float
  , _paddle2   :: Float
  , _score     :: (Int, Int)
  , _vectors   :: [Vector]

  -- Since gloss doesn't cover this, we store the set of pressed keys
  , _keys      :: Set Key
  }

-- Some nice lenses to go with it
makeLenses ''Pong

-- Renamed tuple lenses for enhanced clarity with points/vectors
_x = _1
_y = _2

initial :: Pong
initial = Pong (0, 0) (0, 0) 0 0 (0, 0) [] empty

-- Calculate the y position at which the ball will next hit (on player2's side)
hitPos :: Point -> Vector -> Float
hitPos (x,y) (u,v) = ypos
  where
    xdist = if u >= 0 then 1 - x else 3 + x
    time  = xdist / abs u
    ydist = v * time
    ypos  = bounce (y + ydist)
    o     = 1 - ballRadius

    -- Calculate bounces iteratively
    bounce n
      | n >  o    = bounce (  2 *o - n)
      | n < -o    = bounce ((-2)*o - n)
      | otherwise = n

-- Difficulty function
accuracy :: Pong -> Float
accuracy p = g . f . fromIntegral $ p^.score._1 - p^.score._2
  where
    -- Scaling function
    f x = 0.04 * x + 0.5
    -- Clamping function
    g = min losingAccuracy . max winningAccuracy

-- Game update logic

update :: Float -> Pong -> Pong
update time = execState $ do
  updatePaddles time
  updateBall time
  checkBounds

-- Move the ball by adding its current speed
updateBall :: Float -> State Pong ()
updateBall time = do
  (u, v) <- use ballSpeed
  ballPos += (time * u, time * v)

  -- Make sure it doesn't leave the playing area
  ballPos.both %= clamp ballRadius

-- Update the paddles
updatePaddles :: Float -> State Pong ()
updatePaddles time = do
  p <- get

  let paddleMovement = time * paddleSpeed
      keyPressed key = p^.keys.contains (SpecialKey key)

  -- Update the player's paddle based on keys
  when (keyPressed KeyUp)   $ paddle1 += paddleMovement
  when (keyPressed KeyDown) $ paddle1 -= paddleMovement

  -- Calculate the optimal position
  let optimal = hitPos (p^.ballPos) (p^.ballSpeed)
      acc     = accuracy p
      target  = optimal * acc + (p^.ballPos._y) * (1 - acc)
      dist    = target - p^.paddle2

  -- Move the CPU's paddle towards this optimal position as needed
  when (abs dist > paddleHeight/3) $
    case compare dist 0 of
      GT -> paddle2 += paddleMovement
      LT -> paddle2 -= paddleMovement
      _  -> return ()

  -- Make sure both paddles don't leave the playing area
  paddle1 %= clamp (paddleHeight/2)
  paddle2 %= clamp (paddleHeight/2)

-- Clamp to the region (-1, 1) but with padding
clamp :: Float -> Float -> Float
clamp pad = max (pad - 1) . min (1 - pad)

-- Check for collisions and/or scores
checkBounds :: State Pong ()
checkBounds = do
  p <- get
  let (x,y) = p^.ballPos

  -- Check for collisions with the top or bottom
  when (abs y >= edge) $
    ballSpeed._y %= negate

  -- Check for collisions with paddles
  let check paddle other
        | y >= p^.paddle - paddleHeight/2 && y <= p^.paddle + paddleHeight/2 = do
            ballSpeed._x   %= negate
            ballSpeed._y   += 3*(y - p^.paddle) -- add english
            ballSpeed.both *= speedIncrease
        | otherwise = do
          score.other += 1
          reset

  when (x >=  edge) $ check paddle2 _1
  when (x <= -edge) $ check paddle1 _2

  where
    edge = 1 - ballRadius

-- Reset the game
reset :: State Pong ()
reset = do
  ballPos .= (0, 0)
  ballSpeed <~ nextSpeed

-- Retrieve a speed from the list, dropping it in the process
nextSpeed :: State Pong Vector
nextSpeed = do
  v:vs <- use vectors
  vectors .= vs
  return v

-- Drawing a pong state to the screen

draw :: Pong -> Picture
draw p = scale gameSize gameSize $ Pictures
  [ drawBall   `at` p^.ballPos
  , drawPaddle `at` (-paddleX, p^.paddle1)
  , drawPaddle `at` ( paddleX, p^.paddle2)

  -- Score and playing field
  , drawScore (p^.score) `at` (-0.1, 0.85)
  , rectangleWire 2 2
  ]
  where
    paddleX = 1 + paddleWidth/2
    p `at` (x,y) = translate x y p; infixr 1 `at`

drawPaddle :: Picture
drawPaddle = rectangleSolid paddleWidth paddleHeight

drawBall :: Picture
drawBall = circleSolid ballRadius

drawScore :: (Int, Int) -> Picture
drawScore (x, y) = scale textSize textSize . text $ show x ++ " " ++ show y

-- Handle input by simply updating the keys set

handle :: Event -> Pong -> Pong
handle (EventKey k s _ _) = keys.contains k .~ (s == Down)
handle _ = id

-- The main program action

main = do
  v:vs <- startingSpeeds
  let world = ballSpeed .~ v $ vectors .~ vs $ initial
  play display backColor fps world draw handle update

  where
    display   = InWindow "Pong!" (windowWidth, windowHeight) (200, 200)
    backColor = white
    fps       = 120

-- Generate the random list of starting speeds

startingSpeeds :: IO [Vector]
startingSpeeds = do
  rs <- randomRs (-initialSpeed, initialSpeed) <$> getStdGen
  return . interleave $ filter ((> 0.2) . abs) rs

  where
    interleave :: [a] -> [(a,a)]
    interleave (x:y:xs) = (x,y) : interleave xs
    interleave _        = []